Large areas of open space, such as a farm stead, a parking lot or deck of a parking garage, or a roadway, require sufficient lighting to allow for safe travel of vehicles and persons through the space at all times including periods of reduced natural lighting, such as nighttime, rainy, or foggy weather conditions. A luminaire for rural areas, an outdoor parking lot or covered parking deck, a roadway, etc. must illuminate a large area of space in the vicinity of the luminaire while controlling glare so as not to distract drivers. In some applications such as roadway, street, or parking lot lighting, it may be desirable to illuminate certain regions surrounding a light fixture while maintaining relatively low illumination of neighboring regions thereof. For example, along a roadway, it may be preferred to direct light in a lateral direction parallel with the roadway while minimizing illumination in a longitudinal direction toward roadside houses or other buildings. Still further, such a luminaire should be universal in the sense that the luminaire can be mounted in various enclosed and non-enclosed locations, on poles or on a surface (such as a garage ceiling), and preferably present a uniform appearance.
Advances in light emitting diode (LED) technology have resulted in wide adoption of luminaires that incorporate such devices. While LEDs can be used alone to produce light without the need for supplementary optical devices, it has been found that optical modifiers, such as lenses, reflectors, optical waveguides, and combinations thereof, can significantly improve illumination distribution for particular applications. Improved consistency in the manufacture of LEDs along with improvements in the utilization of mounting structures to act as heat sinks have resulted in luminaires that are economically competitive and operationally superior to the conventional incandescent and fluorescent lighting that has been the staple of the industry for decades. As the use of LEDs has matured from their use in warning and other signals to general lighting fixtures, it has become necessary to develop optics that allow for the dispersion of the harsh, intensely concentrated beam of light emitted by the LED into a softer, more comfortable illumination that presents a uniform and even appearance. One way of attaining a more uniform appearance is to control the light rays generated by the LEDs so as to redirect the light rays through and/or out of an optic so that the light presents a uniform appearance when it exits the optic. Redirecting light through the optic can be accomplished through the use of refractive surfaces at a refractive index interface.
The numerous locations and the environmental disparities therebetween have led to sealing and weather-proofing techniques for LED luminaires. Sealing and weather-proofing is useful to protect LEDs, LED driver circuitry, control circuitry, sensors, other circuitry, and/or other sensitive components of the luminaire. Sometimes sealing and weather-proofing techniques result in volumes within luminaires becoming susceptible to damage resulting from pressure, temperature, and humidity differences between one or more volumes within the luminaires and/or the outside environment.
One practice for equalizing environmental parameters between luminaire compartments utilizes a plug with a gas permeable membrane, such as Gore-Tex®brand material or another suitable membrane material, disposed therein. Such a plug provides for pressure equalization across an otherwise air-tight gasket, however, plugs of this type may add expense and are susceptible to clogging. An improved method and arrangement for providing vent(s) and/or venting of one or more volumes within luminaire(s) is desirable within the field of LED lighting.